This invention relates to the preparation of 1,2-bis(4-hydroxyaryl)ethanes. More specifically, it relates to a one-step dehydrohalogenation-rearrangement-hydrogenation of 1,1-bis(4-hydroxyaryl)-2-haloethanes under suitable conditions to yield the corresponding 1,2-bis(4-hydroxyaryl)ethanes, particularly 1,2-bis(4-hydroxyphenyl)ethane from 1,1-bis(4-hydroxyphenyl)-2-chloroethane.
The dehydrohalogenation-rearrangement of 1,1-bis(4-hydroxyaryl)-2-haloethanes to 4,4'-dihydroxystilbenes is known in the art. The reaction is effected under strongly basic and rather drastic conditions by heating the compound in a solution of potassium hydroxide or sodium hydroxide in methanol or ethanol at the boiling point of the solvent, followed by further heating of the dehydrohalogenated product in a high-boiling solvent selected from the group consisting of ethylene glycol, diethylene glycol monomethyl ether (methyl carbitol), and nitrobenzene to the boiling point of such solvent. The reaction may also be effected in one step by heating the 1,1-bis(4-hydroxyaryl)-2-haloethane directly in a solution of potassium hydroxide or sodium hydroxide in a high-boiling solvent selected from the above list. These processes of preparing 4,4'-dihydroxystilbenes are disclosed in Sieber, U.S. Pat. No. 3,624,162. However, it is apparent that if the corresponding saturated compounds, 1,2-bis(4-hydroxyaryl)ethanes, are desired, a separate hydrogenation step must be employed. The procedural requirements associated with the separate hydrogenation step-first, production and isolation of the 4,4'-dihydroxystilbene, and second, hydrogenation of the 4,4'-dihydroxystilbene--are very time consuming and inconvenient. Moreover, the procedure is not easily adapted to large technical scale operations.
The disadvantages encountered in the strongly basic, high-boiling solvent processes of the prior art are overcome by the discovery that the dehydrohalogenation-rearrangement-hydrogenation of 1,1-bis(4-hydroxyaryl)-2-haloethanes can be readily accomplished in a one-step process under suitable acidic reaction conditions to yield 1,2-bis(4-hydroxyaryl)ethanes.